GOP mayoral candidate Joe Lhota's promise about extending the R subway line to Staten Island misses the long-forgotten proposed tunnel between 68th Street in Bay Ridge and St. George.

The concept was to extend subway service from Brooklyn to Staten Island. Ground was broken with entrances at both ends in the 1920s, but the project quickly ran out of money and was abandoned to history.

When living on Shore Road in Brooklyn, friends and I would look to no avail in attempting to find the abandoned site filled in decades earlier. Flash forward 90 years later and we have the proposed Cross Harbor Freight Tunnel project.

Construction of any new freight or public transportation tunnel or bridge project can take decades to realize before the project provides any beneficial use.

Construction for the Second Avenue subway began in the 1960s. The latest completion date for the first segment between 63rd and 96th streets is 2016 at a cost of $4.5 billion.

Construction for the original tunnel to support bringing the Long Island Rail Road into Grand Central Station began in the 1960s. The latest completion date is now 2019, with a cost of $9 billion.

At the end of the day, just like the long-abandoned Brooklyn to Staten Island subway, don't count on riding the R train to Staten Island in your lifetime.